1. Field
Embodiments relate to a multi-sector antenna, a multi-band multi-sector antenna, and systems including the same.
2. Related Art
In a wireless telecommunications system, a geographic area serviced by the wireless telecommunications system is divided into spatially distinct areas called “cells”. Cells are typically further divided into multiple ‘sectors’. For example, often each of the cells are divided into three equal area sectors. Typically, each cell contains a base transceiver station (BTS) that uses transceivers (TRXs) and antennas to facilitate wireless communication between user equipment (UE) and a network. The transceivers may include one or more receivers and transmitters and may be packaged in a Remote Radio Heads (RRHs). A RRH generally contains two or more transceivers that are each connected to a duplex filter, thus enabling each transceiver to support simultaneous downlink transmission and uplink reception via a single antenna.
A BTS may also be referred to as a radio base station (RBS), node B (in 3G Networks) or, simply, a base station (BS). Examples of UEs include devices like mobile phones, computers with wireless Internet connectivity, and other devices. The network can be any wireless communication network (e.g., GSM, CDMA, etc.).
The antennas may be housed in an enclosure that protects the antennas from environmental conditions or conceals the antenna's electronic equipment from public view. The enclosure may be referred to as a “radome”. The enclosure is often constructed of a material that is transparent to radio waves and inhibits icing from accumulating on its surface. For instance, the enclosure may be made of a fiberglass material.
Basic Antenna
The simplest antenna technology is a single input, single output (SISO) antenna, which refers to a wireless communications system in which one antenna is used for transmission (e.g., a single ‘input’ into the transmission channel) and one antenna is used for reception (e.g., a single ‘output’ out of the transmission channel). The transmission channel may be a downlink channel (from the BTS's transmitter(s) to the UE's receiver(s)) or an uplink channel (from the UE's transmitter(s) to the BTS's receiver(s)). While relatively simple to design, SISO systems are vulnerable to problems caused by multipath fading effects.
Multipath fading effects result when an electromagnetic field (EM field) meets obstructions such as hills, canyons, buildings, and utility wires, which results in the EM field scattering (reflecting), and thus taking multiple paths to reach its destination, resulting in random phase shifts between the multiple signal paths. When a source sends a Radio Frequency (RF) signal that encounters scattering, the recombination of the multiple RF paths' signals with various phases causes Rayleigh fading effects. When the signals combine into one signal at the receiving antenna, because the signals are out of phase, the effective signal is attenuated. When the attenuation is severe, the signal may be below the receiver's minimum discernible signal level, and the receiver may not be able to successfully receive and decode the original signal. In a wireless telecommunications system, such multipath fading can cause a reduction in coverage area, a reduction in achievable data speeds and an increase in the number of errors in processing the signal.
Diversity
To avoid multipath fading effects, systems are available to improve signal quality by using a plurality of antennas in combination with diversity techniques. Diversity techniques can be used to combine the signals received from the multiple antennas, drastically reducing the probability of fading, because both antennas likely will not experience simultaneous severe fading attenuation.
Diversity techniques can be used for reception and/or transmissions from the multiple antennas. Various terminology is used to describe different diversity techniques. For example, a single input, multiple output (SIMO) technique (uplink or downlink) refers to a diversity technique having a single transmitter antenna (single input) and multiple reception antennas (multiple output) (also known as diversity reception) utilizing any number of separate reception antennas. A multiple input, multiple output MIMO technique (uplink or downlink) refers to a technique including both multiple transmitter antennas (multiple coded transmission signals) and multiple reception antennas.
The multiple reception antennas may provide two-way diversity or four-way diversity depending on the number of independent (or decorrelated) signals provided from the separate antennas.
Each of the multiple antennas used to provide the separate diverse signals can contain multiple antenna elements (e.g., dipole elements). In dipole antennas, a plurality of polarized dipole elements (typically, four to ten elements) are equally spaced and vertically stacked to achieve directivity (antenna gain), thus each antenna may actually be an array of antenna elements. The dipoles may be arranged such that the antenna is either a linear dipole antenna (one element) or dual slant/cross-polarized dipole antenna (twin elements located together).
FIG. 1 illustrates different linear dipole antenna array arrangements.
As illustrated in FIG. 1, in a linear array of dipole antennas 100, the dipole elements are all of the same polarization. These dipole elements may be arranged in an array of vertically polarized dipole elements 110. Alternatively, the dipole elements may be arranged in an array of horizontally polarized dipole elements 120. In antenna arrays that utilize linear arrays of dipole elements, all of the dipole elements receive the same polarization and thus having the same fading behavior (e.g., correlated fading statistics). Therefore to achieve sufficient diversity (independent fading statistics), multiple discrete linear dipole antenna arrays are spaced a distance apart in a technique known as a space diversity (horizontal spatial separation of the antennas).
In space diversity, the antennas are spaced a sufficient horizontal distance apart to ensure that the Rayleigh fading that each array experiences will be independent (decorrelated). In more detail, because of the different physical location of the arrays, the phases of the signals traveling different paths that are recombined are different enough that the apparent fading will be different. However, the minimum distance required between the antenna arrays to ensure independent fading effects is on the order of seven to ten lambda λ (where λ is the wavelength of the RF signal). This minimum distance between the antenna arrays makes the use of a single integrated structure, such as a radome, to house the two antenna arrays impractical because a structure of such size may be visually imposing, heavy and may create a large surface area that is susceptible to wind loading. Therefore, the installation of multiple antenna arrays using spatial diversity generally requires multiple structural enclosures (e.g., separate radomes) resulting in increased costs and more complex installations when compared to single enclosures.
FIGS. 2A and 2B illustrate a conventional antenna installation utilizing space diversity.
As illustrated in FIG. 2A, a conventional antenna structure is mounted on a cellular boom 250 to achieve spatial diversity. FIG. 2B is a three-dimensional view of the conventional antenna structure of FIG. 2A. In the conventional antenna structure, to achieve spatial diversity, a first antenna array 210a and a second antenna array 210b are mounted on the face of the cellular boom 250 and separated from each other by a distance D, where the distance D is a distance sufficient to achieve sufficient spatial diversity between the two antenna arrays 210/210b. The required separation distance D (e.g., seven to ten lambda λ), may make the use of a single integrated structure to house both the first antenna array 110a and the second antenna array 110b impractical. Therefore, in the conventional antenna structure to obtain spatial diversity, the first antenna array 210a is protected by a first enclosure 230a and the second antenna array 210b is protected by the second enclosure 230b. 
To eliminate the need for spacing between the two antenna arrays, and thus separate enclosures, as required for a diversity scheme that utilizes linear dipole antennas, while still achieving adequate decorrelation, cross-polarized dipole antennas may be used.
FIG. 3 illustrates different various cross-polarized antenna array arrangements.
As illustrated in FIG. 3, in cross-polarized antennas 300, the elements that make up the antenna array are orthogonally polarized in a scheme known as polarization diversity. In polarization diversity, two-way diversity is achieved by pairing two complementary polarized antenna elements together into a single structure.
In the cross-polarized antenna array the dual polarized elements may be a dual slant cross polarized antenna 310, in which the polarized elements cross each other in a slant (e.g., +45 degrees and −45 degrees). Alternatively, the array of dual polarized elements may be a vertical/horizontal cross polarized antenna 320 in which the polarized elements cross each other vertically and horizontally. In additional to dual-slant and vertical/horizontal cross-polarized antennas, the dual polarized elements may be arranged to provide circular polarization (not shown). The circular polarization may be either right hand circular polarization (RHCP) or left hand circular polarization (LHCP). Each of the polarized elements in the cross-polarized stack of elements has a port, resulting in the cross-polarized antenna array having two ports (e.g., connections), a first port 340 for one polarization and a second port 350 for the other polarization. The cross-polarized antenna configuration provides two-way diversity without requiring the large spatial separation of the antenna arrays that is required in spatial diversity. Thus, the two sets of antenna elements may be packaged together in one structure, eliminating the requirement for multiple separate antenna structures.
Dual polarized antennas provide only two-way diversity, because there are only two orthogonal polarizations. If four-way diversity is desired, a pair of cross-polarized antennas may be required to achieve both spatial diversity and polarization diversity. The minimum horizontal spacing between the pair of cross-polarized antennas necessary to achieve adequate spatial diversity may again require a system having multiple structural enclosures in order to be practical.